The process of making grease has remained largely unchanged for several decades. Recent developments, however, hold the promise of some major changes for both the materials and the processes employed, and suggest a change in the overall grease making approach. Since the majority of the grease produced worldwide is based upon the use of either lithium or lithium complex, most of these efforts tie into the production of lithium based greases. Simultaneously, there has been a growing interest in the production of biobased and biodegradable greases, using vegetable oils as the base oil. The use of these newer raw materials has introduced a different level of complexity, and sometimes unpredictability to grease making. For soap based greases, the majority of the processes are similar and require reacting the base oil with soap as a thickener, at high temperatures typically exceeding 200° C.
Interesting new processes for grease making have also been attempted, some of which have shown success in increasing the predictability of final products. Those processes include:                a) introduction of pressurized contactors        b) introduction of continuous (vs. batch) processes        c) alternative heating techniques        
Finally, a promising change in the manufacturing of grease is the introduction of vegetable oils as the base greases. Vegetable oils in general are reacted with the lithium thickener in the same way that petroleum base oils are. The University of Northern Iowa's National Ag-Based Lubricants Center (UNI-NABL) has been a leading research center in the creation of manufacturing processes and biobased greases made from vegetable oils. Several commercial grease products including large volumes of rail curve grease made from soybean oils owe their origin to UNI-NABL. Since vegetable oils, in general, range in viscosity from 35-45 cSt at 40° C., UNI-NABL processes have included introduction of some higher viscosity vegetable oils, to increase the viscosity of the starting base oil.
Vegetable oils have a uniquely different behavior when exposed to high temperatures. In the case of some vegetable oils, once the oil temperature exceeds 150° C. (300° F.), the oil begins to oxidize rapidly and if steps are not taken to remedy this rapid oxidation, the product will begin to polymerize, resulting in irreversible change. In such cases, the product could partially or fully polymerize or change state from a soap into a polymer with no or little lubrication value. But, several methods exist for stabilizing soybean or other vegetable oils so they can be reacted with lithium and produce stable greases. The use of high oleic vegetable oils is often employed to improve the oxidation stability of the final product. Vegetable oils, due to their higher viscosity index, present a more stable body when exposed to high temperatures. As a result, properly formulated vegetable oil-based grease would show more stable body in use and would not thin down as fast as comparable mineral oil based greases when exposed to high temperatures.
What is clearly needed, however, are new and improved methods for manufacturing soap, and in turn, greases that are based upon such soaps, in a manner that provides ever better efficiencies and products.